Linear polymers of carbon monoxide with one or more olefinically unsaturated aliphatic compounds are made up of polymer units from carbon monoxide and units from the olefinically unsaturated compounds which are present in a substantially alternating arrangement. These linear polymers can be prepared by contacting the monomers at elevated temperature and pressure with a catalyst composition which comprises a Group VIII metal compound, a phosphorus bidentate ligand, an acid with a pKa&lt;2 and an organic oxidizing agent.
For some applications it may be desirable to have such linear alternating polymers in which optionally substituted phenyl groups occur as side groups linked to the main chains. Attempts using the above-mentioned catalyst compositions to prepare such polymers from a monomer mixture that besides carbon monoxide contains styrene and/or one or more substituted styrenes have had little success up to now. Although these catalyst compositions are eminently suitable for the preparation of linear alternating polymers of carbon monoxide with one or more olefinically unsaturated aliphatic compounds, they have been found less suitable for the preparation of linear alternating polymers of carbon monoxide with styrene and/or with one or more substituted styrenes.
In the course of an investigation concerning these polymers carried out previously by the applicant it was found that starting from monomer mixtures which besides carbon monoxide contain styrene and/or one or more substituted styrenes, linear alternating polymers can be prepared, provided that the phosphorus bidentate ligand in the above-described catalyst compositions is replaced by one of the following three bidentate ligands.
1) a nitrogen bidentate ligand with the general formula ##STR1## wherein X and Y represent identical or different organic bridging groups and X and Y each contain three or four atoms in the bridge, and at least two of which are carbon atoms,
2) a sulphur bidentate ligand with the general formula (R.sub.1)S-R-S(R.sub.2) in which R.sub.1 and R.sub.2 represent identical or different optionally polar-substituted hydrocarbon groups and R is a divalent organic bridging group containing at least two carbon atoms in the bridge, and
3) a nitrogen bidentate ligand in which a (R.sub.3)N group occurs, the nitrogen atom of which is connected solely via a non-aromatic double bond with a carbon atom of a hydrocarbon bridging group R.sub.4 and in which moreover either (i) a (R.sub.5)N group occurs, the nitrogen atom of which is connected via a double bond with a carbon atom of the bridging group R.sub.4, or (ii) a (R.sub.5)(R.sub.6)N group is present, the nitrogen atom of which is connected via a single bond with a carbon atom of the bridging group R.sub.4, wherein in the above-mentioned groups R.sub.3 represents a monovalent hydrocarbon group and R.sub.5 and R.sub.6 are identical or different hydrocarbon groups, optionally the same as R.sub.3.
In the polymer preparations carried out until recently, use was made of, inter alia, catalyst compositions which contained one of the following bidentate ligands: 2,2'-bipyridine, 1,10-phenanthroline, 1,2-bis(ethylthio)ethane, cis-1,2-bis(benzylthio)ethene and (cyclohexyl)N.dbd.C(H)--C(H).dbd.N(cyclohexyl). Trifluoroacetic acid or para-toluenesulphonic acid were usually used as acids. The quantity of organic oxidizing agent in the catalyst compositions was, as a rule, 100-300 mol per g.atom Group VIII metal. The above-mentioned polymerizations were usually performed at a temperature selected between 50.degree. and 100.degree. C. such as to satisfy the practical requirement that the resulting reaction rate should be at least 50 g polymer/(g Group VIII metal.hour). Polymers were obtained from these polymerizations having an average molecular weight, calculated as number average (M.sub.n), of less than 20,000.
For some applications it may be desirable to have such polymers with an M.sub.n of above 30,000. An investigation has been carried out by the applicant concerning the preparation of these polymers. The investigation showed that it is not possible to prepare such polymers at an acceptable reaction rate using the previously used catalyst compositions. Although it is possible, by reducing the reaction temperature, to obtain some increase in the M.sub.n of the polymers, this is accompanied by such a sharp reduction in the reaction rate that very soon the desired reaction rate of 50 g/(g.hour) is no longer satisfied. In general, it can be stated that with the catalyst compositions used to date it has not been found possible in the preparation of linear alternating polymers of carbon monoxide with styrene and/or with one or more substituted styrenes to prepare polymers with an M.sub.n of above 30,000 at a reaction rate of least 50 g/(g.hour).
In the course of continued research by the applicant into this subject it has now surprisingly been found that both the previously mentioned criteria can be satisfied if a catalyst composition is used which contains a nitrogen bidentate ligand mentioned under (1) above and an acid with a pKa&lt;-3. Polymers of the present type with an M.sub.n of above 30,000 are novel.